S YNCHRONOUS & 24-Nov-2010 A SYNCHRONOUS D ATA T RANSFER - - PowerPoint PPT Presentation

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S YNCHRONOUS & 24-Nov-2010 A SYNCHRONOUS D ATA T RANSFER www.eazynotes.com Maninder Kaur 1 professormaninder@gmail.com S YNCHRONOUS D ATA T RANSFER 24-Nov-2010 In a digital system, the internal operations are synchronized by means of

SLIDE 1

SYNCHRONOUS & ASYNCHRONOUS DATA TRANSFER

Maninder Kaur

professormaninder@gmail.com

24-Nov-2010

www.eazynotes.com

SLIDE 2

SYNCHRONOUS DATA TRANSFER

 In a digital system, the internal operations are

synchronized by means of clock pulses supplied by a common pulse generator.

 In a computer, CPU and an I/O interface are

designed independently of each other.

 If the registers in the interface share a common

clock with the CPU registers, the data transfer between two units are said to be synchronous.

24-Nov-2010

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ASYNCHRONOUS DATA TRANSFER

 In a computer system, CPU and an I/O interface

are designed independently of each other.

 When internal timing in each unit is independent

from the other and when registers in interface and registers of CPU uses its own private clock.

 In that case the two units are said to be

asynchronous to each other. CPU and I/O device must coordinate for data transfers.

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METHODS USED IN ASYNCHRONOUS DATA TRANSFER

 Strobe Control: This is one way of transfer i.e. by means

f strobe pulse supplied by one of the units to indicate to

the other unit when the transfer has to occur.

 Handshaking: This method is used to accompany each

data item being transferred with a control signal that indicates the presence of data in the bus. The unit receiving the data item responds with another control signal to acknowledge receipt of the data.

24-Nov-2010

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STROBE CONTROL

 Strobe control method of data transfer uses a single

control signal for each transfer. The strobe may be activated by either the source unit or the destination unit.

 Source Initiated Strobe  Destination Initiated Strobe

Source Unit Destination Unit Data bus Strobe

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SOURCE INITIATED STROBE

 The data bus carries the binary information from source

unit to the destination unit as shown below.

 The strobe is a single line that informs the destination

unit when a valid data word is available in the bus.

Valid data

Data Strobe Timing diagram

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SOURCE INITIATED STROBE

 The source unit first places the data on the bus.  After a brief delay to ensure that the data settle to a

steady value, the source activities the strobe pulse.

 The information of the data bus and the strobe

signal remain in the active state for a sufficient time period to allow the destination unit to receive the data.

 The source removes the data from the bus for a

brief period of time after it disables its strobe pulse.

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DESTINATION INITIATED STROBE

 First, the destination unit activates the strobe pulse, informing

the source to provide the data.

 The source unit responds by placing the requested binary

information on the unit to accept it.

 The data must be valid and remain in the bus long enough for

the destination unit to accept it.

 The falling edge of the strobe pulse can be used again to

trigger a destination register.

 The destination unit then disables the strobe. The source

removes the data from the bus after a predetermined time interval.

24-Nov-2010

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SLIDE 9

DESTINATION INITIATED STROBE

Valid data

Data Strobe Timing diagram Block diagram Source Unit Destination Unit Data bus Strobe

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HANDSHAKING

 In case of source initiated data transfer under strobe

control method, the source unit has no way of knowing whether destination unit has received the data or not.

 Similarly, destination initiated transfer has no method of

knowing whether the source unit has placed the data on the data bus.

 Handshaking mechanism solves this problem by

introducing a second control signal that provides a reply to the unit that initiate the transfer.

 There are two control lines in handshaking technique:  Source to destination unit  Destination to source unit

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SOURCE INITIATED TRANSFER

 Handshaking signals are used to synchronize the

bus activities.

 The two handshaking lines are data valid, which is

generated by the source unit, and data accepted, generated by the destination unit.

 The timing diagram shows exchange of signals

between two units.

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SLIDE 12

SOURCE INITIATED TRANSFER

Block diagram Source Unit Destination Unit Data bus Data valid Data accepted

Valid data

Data Strobe Data accepted Timing diagram

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SOURCE INITIATED TRANSFER USING HANDSHAKING

 The sequence of events:  The source unit initiates the transfer by placing the data

n the bus and enabling its data valid signal.

 The data accepted signals is activated by the

destination unit after it accepts the data from the bus.

 The source unit then disables its data valid signal, which

invalidates the data on the bus.

 The destination unit the disables its data accepted

signal and the system goes into its initial state.

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SOURCE INITIATED TRANSFER USING HANDSHAKING

Place data on bus. Enable data valid Accept data from bus. Enable data accepted Disable data valid. Invalidate data on bus. Disable data accepted. Ready to accept data.

Destination Unit Source Unit Sequence of events

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SLIDE 15

DESTINATION INITIATED TRANSFER USING HANDSHAKING

 In this case the name of the signal generated by the

destination unit is ready for data.

 The source unit does not place the data on the bus

until it receives the ready for data signal from the destination unit.

 The handshaking procedure follows the same

pattern as in source initiated case. The sequence of events in both the cases is almost same except the ready for signal has been converted from data accepted in case of source initiated.

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DESTINATION INITIATED TRANSFER

Block diagram Source unit Destination unit Data bus Data valid Ready for data Ready for Data Data valid Data bus

Timing diagram

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DESTINATION INITIATED TRANSFER USING

HANDSHAKING

Place data on bus. Enable data valid. Ready to accept data. Enable ready for data Disable data valid. Invalidate data on bus. Accept data from bus. Disable ready for data.

Destination Unit Source Unit

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